Application of life cycle assessment to the LCA case studies single superphosphate production

Abstract

There is a competition between wet and thermal routes for phosphate fertilizers manufacture. In the Brazilian case, the thermal route is represented by thermophosphate. This fertilizer is considered the most adequate one for Brazilian agricultural conditions; its main restriction is the intensive consumption of energy necessary for its production. The wet route uses sulfuric acid to direcdy produce the single superphosphate (SSP) or the intermediate phosphoric acid, which will be used to result in triple superphosphate (TSP) and ammonium phosphate production. The main restriction of the wet route is the large amount of phosphogypsum generated in phosphoric acid production. Envisaged is an environmental comparison of both routes using LCA methodology. This paper presents the LCA for SSP production. The goal of the study is to establish the Environmental Profile of this fertilizer. Eight impact categories were selected for the study. The system boundaries was defined for a ‘cradle to gate’ approach, including extraction of natural resources, intermediate products, and production. The SSP system (single superphosphate) comprises the stages of mining and concentration of the phosphate rock, elemental sulfur extraction, production of sulfuric acid, and manufacture of single superphosphate. The LCI was performed considering the production of 1.0 ton of SSP (single superphosphate) as a Functional Unit. The data collected were developed for different producing companies, all of them located in the same regional area. Allocation criteria of energy and mass were applied to the production of sulfuric acid and manufacture of single superphosphate. The transportation step included either the transport of the mined phosphated rock to the concentration plant or the transport of the phosphate concentrate to the SSP unit. The accomplishment of an LCA to SSP production identified the GWP and EP as its meaningful environmental impacts. In reference to global warming, the transportation step was the greatest contributor agent, while the losses of POb4-from the SSP manufacturing were the main cause of EP. The most important contribution in terms of water consumption was observed in the concentration step. Finally, the self sufficiency of the sulfuric acid production in energetic terms must be highlighted. The knowledge of the environmental profile of fertilizers is necessary to support LCA studies of agricultural products, a relevant raw material source for many industrial sectors. The method used here may be important for modelling other LCA fertilizer studies. As most of the agricultural raw materials are transferred among different countries, comparisons of the environmental profiles of fertilizers in developed and developing countries are needed.